Torque transmitting eddy-current apparatus



1954 w. s. BURDICK ETA].

TORQUE TRANSMITTING EDDY-CURRENT APPARATUS Filed May 1, 1952 2Sheets-Sheet l "/1! a INVENgORS BY W 6. 7 7:4

1954 w. s. BURDICK ETAL 2,663,922

TORQUE TRANSMITTING EDDY-CURRENT APPARATUS I \N a W INVENTORJ uzz J. M43 y M6. 7

Patented Feb. 9, 1954 TORQUE TRANSMITTING EDDY-CURRENT APPARATUS Will S.Burdick, Wauwatosa, and Robert E. Meyer, Shorewood, Wis., assignors toHarnischfeger Corporation, Milwaukee, Wis., a corporation of WisconsinApplication May 1, 1952, Serial No. 285,434

4 Claims.

This invention relates to eddy current torque transmitting apparatus inwhich a drum of magnetic material is mounted for relative rotation withrespect to a ma netic field member and it resides more specifically inan improvement in the drum portion of such apparatus wherein the drum isdivided into segments that may expand circumferentially with temperaturechanges to relieve the drum of thermally induced stresses and tominimize thermally induced changes in drum diameter, the segments eachbeing anchored at their centers to a drum support, having sufiicientstrength and rigidity to transmit substantially the entire torquereaction, with expandable overhanging end portions on each side of theanchored center that are connected in turn with the drum support byeasily deflected heat dissipating cooling fins sufliciently yieldable tobe incapable of transmitting the torque reaction and being of such thinsection as to yield without destructive stress occurring therein inresponse to the thermal expansion occurring in the overhanging portionsof said segments.

Eddy current torque transmitting apparatus as is employed for brakes andclutches have high rates of heat generation in the eddy current members.As the torque transmitted increases heat generation correspondinglyincreases and temperatures encountered in the eddy current membersbecome excessive and limit the output of the apparatus. In order tominimize the resulting thermally induced expansion of the heated eddycurrent members the apparatus is designed to rapidly dissipate the heat.It is also desirable that expansion of the eddy current members beprovided for without incurring a material change in air gap dimension.Since it is advantageous to employ small air gaps in order to attainmaximum torque output a variation in the gap due to thermal expansion ina radial direction may cause either a destructive binding of the fieldand eddy current members or a large relative change in the gap dimensionthat materially affects the torque output values.

To provide a low inertia member and to effectively dissipate heat due tothe induced eddy currents the eddy current member has been formed as athin walled drum supported from a hub by a plurality of spaced fins. Thedrum has been circumferentially segmented to permit circumferentialexpansion and the fins supporting the segments act to both carry heataway from the areas of generation and to transmit the torque reaction ofthe device. Since it is desired that eddy current apparatus of thisnature be utilized primarily as a torque transmitter of maximum capacityper unit of apparatus the fins must necessarily have substantialcross-section in order to transmit the torque Without incurring rupture.The circumferential deflection of the fins is thus limited. Suchdeflection will be resisted and the thermal expansion of the segmentscomprising the drum is therefore ourtailed circumferentially and theradial expansion that accompanies temperature increase is appreciable.

Eddy current drum segments, of reasonable length, permitted to expandunrestrained circumferentially will have a maximum circumferentialdisplacement that may effect fatigue failure in the supporting finsjoined to the segments at the points of such maximum displacement,unless the fin width is made quite small. Thin fins of such reducedWidth are inefiectual for transmission of torque reaction. Resort may bemade to an increased number of fins. This increase however would againrestrain circumferential expansion of the segments. Furthermore, areduction in fin width will permit greater circumferential deflectiondue to torque transmission. This augmented defiection will call forincreased yieldability of the fins if fatigue failure is to be avoided.Consequently a compromise must be made in the choice of fin dimensionthat will restrict circumferential expansion to a degree necessitated bythe attainment of necessary fin strength,

Permissible temperature increase of the drum may be limited for a deviceof given weight and dimension by the rating given the device. Thecapacity, limited in this manner, does not, however, efiectively utilizethe device. It has been the practice to reach a practical compromise ofthe foregoing factors that gives a relatively high capacity withinpermissible limits of temperature rise and fin width and spacing.

It is an object of this invention to provide an eddy current drum for aninduced current torque transmitter that is segmented circumferentiallyto allow circumferential expansion and that will have a minimum ofradial expansion with temperature rise.

It is another object of this invention to providean eddy current drumsegmented circumferentially with each segment thereof supported forunrestricted thermal expansion along its circumferential extent ineither circumferential direction from the center portion that isanchored with respect to a supporting hub.

It is a further object of this invention to prothe accompanying drawingsin vvhidli.2there;;is-.ii.

shown by way of illustration and not of limitation one specific form inwhich .this.invention.

may be embodied.

In the drawings:

Fig. 1 is a longitudinal view in elevation and in section of an inducedcurrent torque transmitter in which this invention is embodied' Fig. 2is a fragmentary top plan view of the.

eddy current member of the: induced current torque transmitter. shown inFigl, and.

' leftofthe fly wheel plate 2.

Fig..'"3 is a .fragmentary end.yiew.'ineleva-. tion of a. portionofthe.eddy.jcurrent andfieldl" members of th'eiinduc'ed.current'torquetrans-.

mitter. shown. in Figfl 1.

Referring .now to the .drawings,..ther,e. is shown in Fig.1 an input ..shaft..l. extendingliori the length of theapparatus. which is adapted .atthe right hand end thereof foriattachnient to anoutput shaft. of a primemover or other driver, not,

shown. At the'left hand end of theinp'ut shaft." I is mounted a circular.fly wheelplatez that-:2.

is keyed to the'shaftLto rotate therewith.) The"? fiy wheel platelz. i'sformed with'a pluralityiof circumferentially spaced radiallyextendingcool ing air ducts 3 andsecured to the peripheralmar" gin ofthe .plate' 2 is .arelatively thin .walled.ci1.- cular cylindrical fieldframe .4. "Seated: against the inner wa1l..of theframe dis an annulartoothed ring 'fi with teeth't circ'umier'entially spacedirom one anotherextending. inwardly'to form pole faces for the fieldmember. Th'eteeth 6are spaced evenly from oneanother and each.

extends in a taper tothe'rlght as shown in l. The taper presents .poleiac'esQtroughlyirus 1 to-triangular configuration. .A second annular.toothed ring. "i, also seated withinthe'field'frame 4, is spaced .to'therightof thering fi to' form a channelbetween the rings .5 and. I.Circunn.

ferentiallyispaced teeth. 8 of. the ring "i extend inwardly. similarlyas the teeth '5 tdform a ring 1 The teeth '8' also .taper' to both ofpole faces. the left and to the right, as shown in Fig.1. Thosealignment with the teeth in of the ring 5} and the teeth 6 of the ring5.

A series of four annular field coils l5 each disposed within one of theannular channels formed by the spaced rings 5, l, 9, and ll and I3provide inagneticifiuxwhen energizedliorseach set of interdigited.t'eeth. r'The flux. pattern .thatis formed by the field member isconventional and well known.

A slip ring assembly IS for the field coils I5 ismounted.onrthelinputrshaft I directly to the A mounting plate llhasfiXedthereon two slip rings :8 and I3 each-of which hasbearingthereupon a crush 29 supportedrrin Wellknowir-lashion and connectedthereof.

Encircling the input shaft lis a pinion sleeve 22 that is mounted forrotation independent.

of the shaft I. Roll'er'bearings and. that seat within the sleeve-22support the shaft I. so that it may rotate freely and the sleeve 22is'in turn m'ountedby roller bearings. 25 and 2% that are housed insuitable mounting brackets 27 and 28 which form a part of any. generalapparatus in conjunction with which the torque trans? mittin'g apparatusof this invention is employed.

Mounted upon and rotatable with the pinion sleeve 22 is'an eddy currentmember.29 disposed I withinthearea circumscribedlby the poleface's ofthep'oleteeths, 8,19,!2 and 14.. Eddy cur-v rent member-29 has a hub'30mounted directly 1 upon the 'pinion'sleeve 22 and joined securely tothehub' 30 Taretwo circular radially extending axially spaced diaphragmplates 3|. Extending. I

betweenand' passingthrough theJplates. 3| to overhangi'beyond the "sameare a number of circumferentially'spaced "heat dissipating tube '32composed of 'amaterial having 'a high heat con ductivity.'"-The"tubes 32are disposed radially inward fromthe'outer periphery of the circular.

plates 3| and are integrally joinedfthereto' to effect anefficienth'eattransfer from the periph eral portions of the plat'es 3| tothetubes' 32.

. Heat spreading from the edges of the plates '31 portions of the teeth.8' extendin'g'to the left fall betweenand are. inte'rdlgited with theteeth .5 of ring '5, so that as'one proceeds ab0 ut..the re-1 sultingring of interlapping pole faces they are" alternately.composedoi.teethBand 82'1" A thirdLa-nnular toothed'ringfiwith inwardly 1.

extending pole teeth to isspaced to, the fright.

of the ring if. The teeth 1H1 are aligned circumferentially with.theteeth/G :of th'eiring 5 and.

are shaped similar. as the teeth 'B'o'f' ring 'l'so as to extend both tothe left. andtofthe"right?" A fourthring H similartotheringslla'nd"Q:isI

disposed at a spaced"distance froirrtheiring fl and the'pole teeth l2thereof; are circumferen' tially aligned with the teeth't oi thering-"l.

will thenbe'retarded from-further flow toward the hub"30."-

Disposed"radially beyond the periphery of the diaphragmpla'tes 31 is asegmented eddy current; drum 33 that forms the rim of the 'eddycurrentmember'29. The drum' 33 is divided both axially andcircumferentially into a plurality'of seg ments*34's'uch that there ispresented four rings of segments, each ring comprisediof segmentsdisposed-in circumferential end to end "position.

Joining the segments 34 tothe diaphragm plates "3| are "a number of twolegged anchorages 35 as is moreclearlyshown in Fig. 3, in whichthe legsmeet'at the pointof juncture with the segments-34 and diverge as theyextend-inwardly toward-the plates 31. As is shown'in Fig-2 eachanchorage 35 extends for the'axial length of the -drurn34 *tofsupportfour axially aligned segments at the approximate" center portion ofeach. The 'supportthusprovided by the an- An annularptoothed outer'ring.fil spaced'to the right ortheringfl that "issimiliar -to the left;

hand outer ring eic'ompletes'the"setof polexpiece members-whicharemounted onth'efield frarne 4 to form-the magnetic-circuitof the fieldmem ber of the apparatus. Teeth-"l4 of 'theringlfi extend to the leftonly-andare in circumferential"- chorages 35 slots 'to rigidly securethe center portion of the respective segments "34 to thediaphragmplate's' 3|, to. provide for the entire transmissionorthe'torque developed by'the ap paratus through anchorage means'for theeddyr current drum 33 that are notsubject tocircumferential"displacementas heating occurs in the drum 33. Theportions of the segments 34 that overhang beyond the rigidly anchoredconnections and extend circumferentially to either side are free toexpand and contract with temperature change, or to be displaced slightlywithout restraint from the supporting means.

Extending radially between the under surfaces of the segments 34 and thediaphragms 3| are a number of thin cooling fins, designated by thereference numerals 36 and 31, that are of high heat conductivity. Fins3'! join with the end portions of the segments 34 and the fins 36 arespaced between the end fins 31 and the twin legged anchorages 35. Thefins 36 and 31 are joined to the respective segments 34 with solid weldsthat effectively conduct heat away from the segments 34 to the fines.The fins 36 and v 31 extend inward from the drum 33 to be anchored tothe diaphragm plates 3| for adequate support and to allow the fins 36and 31 to further act as tension members to restrain the drum segments34 from defieting radially outward.

The longitudinally or axially extending spacings between drum segmentsthat divide the drum 33 into circumferentially extending segments 34 inend to end relation are skewed with respect to the field member of theapparatus in order to reduce magnetic vibrations. The skewing of thegaps between segments gives each segment 34 a parallelogram shaped faceas is shown in Fig. 2. The cooling fins 31, that are connected to theends of the segments 34, are consequently attached to a trailing end ofone segment 34 and the leading end of the circumferentially adjacentsegment 34. Each fin 3! extends across the axial length of the drum 33to be connected in like manner with a pair of segments 34 in each of thefour circumferential rings of drum segments 34. Consequently each fin 31is subject to circumferential displacement in opposite directions as thesegments 34 expand with temperature increase. This is due to theexpansion of trailing edges of the segments 34 in one direction and theexpansion of the leading edges in the opposite direction. A fin 31 isshown in the lower half of Fig. 1, in which there are shown cutouts inthe fin 31 at the points where it crosses from a leading edge to atrailing edge. Cooling fins 3'! formed with such cutouts are extendedradially inwardly to a greater depth than the other fins 36 to providefor sufiicient strength.

The pinion sleeve 22 has integrally formed therewith a pinion 45, whichis disposed between the mounting walls 21 and 28, to provide a powertakeoff from the eddy current apparatus. A gear 46, partially shown, isin mesh with the pinion 45.

Disposed on the right end of the pinion sleeve 22 is a brake assembly38. A hub 39 is joined to the sleeve 22 and a pair of radially extendingdiaphragms 40 extend outward from the hub 39. A plurality of drumsupporting plates 4| are joined to the outer peripheries of thediaphragms 40. A brake drum 42 is supported and joined to the outer endsof the plates 4| and disposed about the brake drum 42 is a brake lining43 and brake band 44 which are supported and operated in well knownmanner, by means not shown.

Upon rotation of the input shaft I the field member, comprising the fiywheel mounting plate 2 and field frame 4 with its field coils l5 andassociated annular toothed rings 5, 1, 9, and I3, likewise rotates.Energization of the field coils I5 creates a field flux which will sweepthrough the segmented eddy current drum 33 in conventional manner toinduce eddy currents therein. Electromagnetic forces will then urge theeddy current member 29 to be likewise set into rotation. A rotation ofthe eddy current member 29 will carry the pinion sleeve 22 therewiththus causing the pinion 45 to deliver output torque to the gear 46. Upondeenergization of the field coils IS the rotation of the shaft 22 and.pinion 45 may be halted by operation of the brake assembly 38. There isthus provided an apparatus of the eddy current type for torquetransmission.

Under heavy duty operating conditions heating within the eddy currentdrum 33 is a limiting factor in the performance of the apparatus. Asmall air gap is desirable and the supporting means for the drum 33 musttransmit the torque reaction without structural failure. Dissipation ofthe heat generated should be rapid. However, the temperature rise in thedrum 33 is nevertheless substantial and the thermally induced stressesmust be relieved. Thus a segmentation of the drum 33 is made. thesegmentation circumferential expansion of the individual segments 34should not be restrained. It is the practice of this invention to anchorthe segments 34 to allow maximum circumferential expansion, so as tolimit radial expansion which would detrimentally afiect air gap widthbetween the field and eddy current members, while simultaneously rigidlyanchoring the segments 34 to eliminate displacement due to torquereaction. To this end a central anchorage is employed for each drumsegment and cooling fins extending from the drum are of thin sectionincapable of transmitting the torque reaction or restrainingcircumferential expansion of the segments.

We claim:

1. In a torque transmitting eddy current apparatus having a field memberwith windings adapted to be excited to establish a magnetic flux and adrum of magnetic material relatively rotatable with respect to saidfield member disposed in flux conducting relation thereto, theimprovement in said drum which comprises a substantially non-deformabledrum support, a plurality of segmental drum shoes arranged in end to endrelation with the surfaces thereof facing said field member and disposedin a substantially common surface of revolution, a single substantiallynon-deformable torque transmitting anchorage for each of said shoessecured to said drum support and each extending therefrom radially to ananchorage with its respective shoe to provide thermally expandableoverhanging shoe portions, and a plurality of thin yieldable heatdissipating fins for the overhanging portions of each of said shoessecured in heat conducting relation to said shoes and extending radiallytherefrom.

2. In a torque transmitting eddy-current apparatus having a field memberwith windings adapted to be excited to establish a magnetic fiux and adrum of magnetic material relatively rotatable with respect to saidfield member disposed in flux conducting relation thereto theimprovement in said drum which comprises a substantially non-deformabledrum support; a plurality of segmental drum shoes spaced from said drumsupport and from one another, said shoes being arranged end to endcircumferentially with the surfaces thereof facing said field memberdisposed in a substantially common sur- To fully benefit from face ofrevolution, a single, substantially nondeformable" "torque;:transmitting anchorage for each of'saidshoessecured to'said drum'support' and extending therefrom" radially to an anchor age with itsrespectiveshoe near the center of said shoe to provideoppositethermally'expand able overhanging end portions, and a plurality of thin yieldable'heat dissipating-fins for the overhanging portions of eachof said shoesse-' I cured in heat conducting relationto said shoes 10 andextendin'gtherefromradially to an attachment witnsaid drum supportthesection of said fins being'insufiicient'to render-the fins capablewithout said'anchorage of transmitting the torque Of'WhlCh the apparatusis capable.

3. In a'torque transmitting eddy-current apin said fins, the section ofsaid fins being insufficient to render thefinscapable :without saidanchorages-of transmitting the torque ofwhich the apparatus is capable."c

4. In a torque transmitting eddy-current 'apa 1 paratus having; a field*member with windings :1 adapted to be excited to:establish"amagneticflux and a drum of magnetic" material relativelyux rotatable withrespect to said 'fieldsmember: disposed in fiux condu'cting relationthereto, thew." improvement in said drumnwhich comprises a shaft-mountedsubstantiallywhom-deformable: drum support a'plurality o'fsegmentedannular drum portionsor alike-diameter: axially:tspaced from oneanotherand'iconcentricallyidisposediin relation to said drum supports-the?segments of paratus having a field member with windings adapted to beexcited to establish a magnetic flux and a drum' of magnetic materialrelatively rotatable-With respect" to said field member dissaid drumsbeing arrangedz end to end;circum.- ferentially and' 'spacedfrom'v'oneanother to permit unrestriced"thermal"expansion,v a singlesubstantially v non-deformable r torque "transmit-7 n time: anchorageforiceach of said; drumv segments? 1 secured"to saidfldrumisupports-ands:extending therefrom.=radial1y to an anchorage with itsre-t spectivesegment neanthe' CEIICGIiiOf said'segment to provideopposite" thermally: expandib'le over-s hanging' endzip'ortions," and51a plurality 'of thin?" yieldable heat dissipatingifins :for' theoverhangi ing portions of each of said 'segmentsisecured inn-i heatconduc'ting'rrelationvto said :shoes' and: eX-:

posed in flux-conductingrelation thereto the improvementin saiddrumwhichcomprises a shaft-mounted substantially non-deformable drum support, aplurality of segmental-drum shoes concentrically disposed in relation tosaid drum support "and spaced therefrom and from one another, saidshoesbeing arranged end to end circumferentially withthe surfacesthereof facing saidfielddisposedin a substantially common surfaceof-revolutionja substantially nontending 1 therefrom?- radially 2170 an"attachment F,

deformable radially tapered-torque transmitting anchorage for each ofsaid-shoes having a base of maximum circumferential width secured tosaid drum support and-"extending therefrom radially mally inducedwdimensional -0hal'lgeSfWJhiChma to an anchorage with its respectiveshoe near the centerof said shoe to provide opposite thermallyexpandable overhanging end portions; and a plurality-0f thin yieldableheat dissipating fins for the overhangingportions of each of said shoesdisposed in radial planes secured inheat conducting relation to saidshoes and extending therefromiradially to ain ;attachrnen-t with 'saiddrum support-"said:fins being sufliciently thin'in a circumferentialdirection in irelationn to thev rnaximurm- Icircumfer-ential' thermallyinduced 1, c

.occur in said 'overhangingrportionsiot said seg mentsr-whereby-omaximumzfibre stress in said"? fins will notexceed' a value asuchr'as to cause:1 fatigue failu1- e= ih-said fins; :the sectioiiof said 5i fins being:insufiicient to render" :the zfins capable 5 without said anchorageszroftransmitting thew torque of which therapparatusais capablemWILLiS.BURDICK.' i- ROBERT E.

References Cited in the file of this patent dimension changesiiwhi'ch'may occur "in said UNITED STATES PATENTS overhanging: portions:zof.:eachnrof wsaid'irshoes N a whereby maximum ifibr'e: stress inrsaidfins'willw 312 ggg not exceed aivalue such asto'cause iatigue failures-22594931 JaeschkeT Y

